The invention relates to location applications for wireless networks, particularly to site survey techniques for wireless networks.
Wireless networks have become increasingly popular as network services are not tied to a specific connection point. It has recently been discovered that observations of a signal quality value in a wireless network, such as signal strength, bit error rate/ratio, signal-to-noise ratio, and the like, can be used to locate a mobile communication device. In the context of the present invention, the term ‘terminal’ refers to a mobile communication device whose location is to be determined.
FIG. 1 schematically illustrates an example of such a positioning technique. A terminal T communicates via base stations BS via a radio interface RI. In this example, the communication is assumed to be radio communication. The terminal T observes signal values at the radio interface RI. Observations O are applied to a probabilistic model PM that models the terminal's wireless communication environment and produces a location estimate LE. As used herein, a terminal is a device whose location is to be determined. The terminal communicates via signals in a wireless network, and signal values in the wireless network are used for determining the terminal's location. For example, the terminal may be a data processing device communicating in a wireless local-area network (WLAN). The data processing device may be a general-purpose laptop or palmtop computer or a communication device, or it may be a dedicated test or measurement apparatus such as a hospital instrument connected to the WLAN. A location, as used herein, is a coordinate set comprising one to three coordinates. In some special cases, such as tunnels, a single coordinate may be sufficient but in most cases the location is expressed by a coordinate pair (x, y or angle/radius).
Mobile communication devices measure signal quality parameters. A good example of a signal quality parameter is signal strength. An acronym RSSI is frequently used to refer to a received signal strength indicator. The RSSI is used, for example, to select a cell or base station.
When a wireless network is set up, it is recommended to carry out a site survey in which such signal quality parameters are determined at various locations to ensure that the wireless network provides adequate coverage. In a normal site survey, the locations in which the measurements are made are known by other means, such as from a floor plan or other map.
A problem underlying the present invention is related to the fact that carrying out the site survey and setting up the probabilistic model are expensive processes.
A site survey means observing some quality parameter of a wireless network. Similar problems exist in observing parameters that are not directly coupled to the wireless network, such as measuring an environmental variable such that the wireless network is used for location estimation and for communicating measurement results, without the network itself being measured. A problem in prior art site survey and other measurement techniques in wireless networks is that they are labour intensive and/or produce inadequate information.